The present invention relates to a heater control apparatus to control a heater as a heating source used for the fixing of an image forming apparatus, and to an image forming apparatus using this control apparatus. Generally, in an image forming apparatus which operates by an electrophotographic method, in order to thermally fix a toner image transferred onto one surface of an image supporter such as a transfer sheet, a fixing device is provided with a fixing heating roller contacted with one surface of the image supporter, and a pressure roller is arranged so as to be pressure contacted with the fixing heating roller.
Then, in a certain kind of fixing device, as the heating source of the fixing heating roller, for example, heater lamps such as a halogen lamp (hereinafter, simply called heater) are respectively provided in upper and lower rollers, and respective heaters are structured in such a manner that their lighting conditions are independently on-off controlled.
As described above, a reason why a plurality of heaters are provided, is as follows: for example, irrespective of the difference of sizes of the image supporter, it becomes possible that the temperature distribution of the fixing heating roller becomes uniform in a predetermined temperature range (hereinafter, called specified temperature range), and the rise time of the temperature of the fixing heating roller is reduced.
(The First Problem)
However, in the fixing device as described above, when a plurality of heaters are lighted, the rush current flows into a lighting circuit of the heater simultaneously when these heaters are lighted. By this rush current, voltage variation is generated in an electric lamp line to which the image forming apparatus is connected.
As a result of such occurrence of the voltage variation in the electric lamp line, there is a problem that flicker (i.e., a sense of flickering) is generated in illumination devices connected to the power line in common with the image forming apparatus, and it is necessary that the degree of this flicker is suppressed in a regulated manner (flicker regulation). For example, in the image forming apparatus, the flicker value (short time flicker value) during the copying operation regulated by the voltage variation amount, is regulated to not more than 1, and the flicker value in the stand-by (long time flicker value) regulated by the generation frequency of the voltage variation is regulated to not more than 0.65.
In this connection, in the fixing device as described above, it is found that both of the short time flicker value and long time flicker value are not suppressed in the regulated range. This problem prominently appears when a heater whose output power is specially high is used.
That is, in the fixing device as described above, when heaters which are turned off, are lighted in the parallel condition, large rush current is generated in the heater lighting circuit, thereby, there is a problem that a bad influence is affected on other devices constituting the image forming apparatus.
Accordingly, in the heater lighting circuit structured by electrically connecting a plurality of heaters to a common AC power source through a plurality of switch elements, it can be considered that each heater is in a parallel connection condition at the time of use, but at the time of lighting, each heater is in a serial connection condition, however, the condition at which condition the connection condition may be switched is not considered.
(The Second Problem)
Further, in the heater lighting circuit structured by electrically connecting a plurality of heaters to a common AC power source through a plurality of switch elements as described above, in the heater lighting circuit structured in such a manner that each heater is in parallel connection condition at the time of use, but at the time of lighting, each heater is in a serial connection condition once, and is switched to a parallel connection condition, when the connection condition of the heater is switched, for example, from the serial connection condition to the parallel connection condition, because the switching of condition of each switch element is simultaneously conducted, a short circuit is formed by the switch element which is turned on to the AC power source, and there is a possibility that a dead short is generated.
In such case, the control in which all switch elements are simultaneously turned off for a predetermined time, is also considered, however, the control becomes complicated, and further, it is forecasted that the problem in which the temperature of the heater is lowered due to the off period, is also generated.
The present invention is attained in order to solve the first problem as described above, and the object of the present invention is to provide a heater control apparatus and an image forming apparatus, by which the excessive current generated when a plurality of heaters are lighted is suppressed, and the flicker generated in other illumination devices connected to the power line common to the heater can be suppressed.
Further, the present invention is attained in order to solve the second problem as described above, and the object of the present invention is, in the case where a plurality of heaters which can be switched between the serial connection condition and the parallel connection condition are provided, to provide a heater control apparatus and an image forming apparatus whose operation has high reliability, by preventing the destruction of switching elements due to a dead short when the connection condition of a plurality of heaters is switched.
Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by heater control apparatus and image-forming apparatus described as follow.
(1) A heater control apparatus for controlling a plurality of heaters, each of which is incorporated in an interior of each of rollers, comprising: a plurality of switching elements to switch flowing paths of electronic currents supplied to the heaters from a common power source; a switching control section to control the switching elements so that a connecting mode of the heaters is changeable between a serial connection mode and a parallel connection mode; and a plurality of temperature detecting devices to detect temperatures of the rollers heated by the heaters, each of the temperature detecting devices corresponding to each of the rollers; wherein, when one of the heaters, incorporated in one of the rollers, is turned on, under a condition that temperatures of other rollers are maintained in a predetermined range, the switching control section controls the switching elements so that the connecting mode of the heaters is changed to the serial connection mode before flowing electronic current into the heaters, and under a condition that temperatures of other rollers are lower than a lowest temperature of the predetermined range, the switching control section controls the switching elements so that the connecting mode of the heaters is changed to the parallel connection mode before flowing electronic current into the heaters, and under a condition that temperatures of other rollers exceed a highest temperature of the predetermined range, the switching control section controls the switching elements so that the one of the heaters is independently turned on.
(2) An image-forming apparatus, which conducts heater-controlling operations for controlling a plurality of heaters, each of which is incorporated in an interior of each of rollers, comprising: a plurality of switching elements to switch flowing paths of electronic currents supplied to the heaters from a common power source; a switching control section to control the switching elements so that a connecting mode of the heaters is changeable between a serial connection mode and a parallel connection mode; and a plurality of temperature detecting devices to detect temperatures of the rollers heated by the heaters, each of the temperature detecting devices corresponding to each of the rollers; wherein, when one of the heaters, incorporated in one of the rollers, is turned on, under a condition that temperatures of other rollers are maintained in a predetermined range, the switching control section controls the switching elements so that the connecting mode of the heaters is changed to the serial connection mode before flowing electronic current into the heaters, and under a condition that temperatures of other rollers are lower than a lowest temperature of the predetermined range, the switching control section controls the switching elements so that the connecting mode of the heaters is changed to the parallel connection mode before flowing electronic current into the heaters, and under a condition that temperatures of other rollers exceed a highest temperature of the predetermined range, the switching control section controls the switching elements so that the one of the heaters is independently turned on.
(3) A heater control apparatus for controlling a plurality of heaters, each of which is incorporated in an interior of each of rollers, comprising: a plurality of switching elements to switch flowing paths of electronic currents supplied to the heaters from a common power source; a switching control section to control the switching elements so that a connecting mode of the heaters is changeable between a serial connection mode and a parallel connection mode; and a rush-current limiting element, coupled into anyone of the flowing paths, to limit a rush-current generated by a short circuit, which would be possibly formed depending on a switching status of the switching elements.
(4) The heater control apparatus of item 3, wherein the rush-current limiting element is a register.
(5) An image-forming apparatus, which conducts heater-controlling operations for controlling a plurality of heaters, each of which is incorporated in an interior of each of rollers, comprising: a plurality of switching elements to switch flowing paths of electronic currents supplied to the heaters from a common power source; a switching control section to control the switching elements so that a connecting mode of the heaters is changeable between a serial connection mode and a parallel connection mode; and a rush-current limiting element, coupled into anyone of the flowing paths, to limit a rush-current generated by a short circuit, which would be possibly formed depending on a switching status of the switching elements.
(6) The image-forming apparatus of item 5, wherein the rush-current limiting element is a register.
(7) The heater control apparatus of item 1, further comprising: a rush-current limiting element, coupled into anyone of the flowing paths, to limit a rush-current generated by a short circuit, which would be possibly formed depending on a switching status of the switching elements.
(8) The heater control apparatus of item 7, wherein the rush-current limiting element is a register.
(9) An image-forming apparatus, which conducts heater-controlling operations for controlling a plurality of heaters, each of which is incorporated in an interior of each of rollers, comprising: a plurality of switching elements to switch flowing paths of electronic currents supplied to the heaters from a common power source; a switching control section to control the switching elements so that a connecting mode of the heaters is changeable between a serial connection mode and a parallel connection mode; a plurality of temperature detecting devices to detect temperatures of the rollers heated by the heaters, each of the temperature detecting devices corresponding to each of the rollers; and a rush-current limiting element, coupled into anyone of the flowing paths, to limit a rush-current generated by a short circuit, which would be possibly formed depending on a switching status of the switching elements; wherein, when one of the heaters, incorporated in one of the rollers, is turned on, under a condition that temperatures of other rollers are maintained in a predetermined range, the switching control section controls the switching elements so that the connecting mode of the heaters is changed to the serial connection mode before flowing electronic current into the heaters, and under a condition that temperatures of other rollers are lower than a lowest temperature of the predetermined range, the switching control section controls the switching elements so that the connecting mode of the heaters is changed to the parallel connection mode before flowing electronic current into the heaters, and under a condition that temperatures of other rollers exceed a highest temperature of the predetermined range, the switching control section controls the switching elements so that the one of the heaters is independently turned on.
(10) The image-forming apparatus of item 9, wherein the rush-current limiting element is a register.
Further, to overcome the abovementioned problems, other image-recording apparatus, embodied in the present invention, will be described as follow:
(11) A heater control apparatus, characterized in that, in the heater control apparatus which is provided with: a plurality of switch elements to switch the supply of the electric power from a common power source; a plurality of heaters which are connected to the common power source through the plurality of switch elements, and respectively housed in rollers; a switching control means for controlling so that, by controlling a condition of each switch element, the plurality of heaters can be switched between the serial connection condition and parallel connection condition; and a temperature detecting means for detecting the temperature of rollers heated by each heater,
in the case where one heater is tried to be lighted, the switching control means controls such that, when the temperature of a roller heated by the other heater is in a predetermined temperature range, one heater is serially connected to the other heater, and lighted, and when the temperature of a roller heated by the other heater is not higher than a predetermined temperature range, the one heater is parallelly connected with the other heater, and lighted, and when the temperature of the roller heated by the other heater exceeds the predetermined temperature range, the one heater is independently lighted.
(12) An image forming apparatus, characterized in that,
in the image forming apparatus, conducting the heater control, which is provided with: a plurality of switch elements to switch the supply of the electric power from a common power source; a plurality of heaters which are connected to the common power source through the plurality of switch elements, and respectively housed in rollers; a switching control means for controlling so that, by controlling a condition of each switch element, the plurality of heaters can be switched between the serial connection condition and parallel connection condition; and a temperature detecting means for detecting the temperature of rollers heated by each heater,
in the case where one heater is tried to be lighted, the switching control means controls such that, when the temperature of a roller heated by the other heater is in a predetermined temperature range, one heater is serially connected to the other heater, and lighted, and when the temperature of a roller heated by the other heater is not higher than a predetermined temperature range, the one heater is parallelly connected with the other heater, and lighted, and when the temperature of the roller heated by the other heater exceeds the predetermined temperature range, the one heater is independently lighted.
In these inventions, in the case where one heater is tried to be lighted,
(a) when the temperature of a roller heated by the other heater is in a predetermined specified temperature range, one heater is controlled in such a manner that it is serially connected to the other heater and lighted,
(b) when the temperature of a roller heated by the other heater is not higher than a predetermined specified temperature range, the one heater is controlled such that it is parallelly connected with the other heater, and lighted, and,
(c) when the temperature of the roller heated by the other heater exceeds the predetermined specified temperature range, it is controlled in such a manner that the one heater is not connected to the other heater and only the one heater is lighted.
When conducted as described above, when a plurality of heaters are lighted in the case of (a), the resistance value is increased by the serial connection, and even when the heater in which the temperature is low and the resistance value is small, is lighted, the rush current is reduced. That is, the generated excessive current is suppressed and the flickers generated in other illumination devices connected to the power line in common with the heaters can be suppressed. Further, in the case of (b), in order to dissolve the low temperature condition, the temperature rise is accelerated by the parallel connection. Further, in the case of (c), the lighting of the other heater is not necessary and only the one heater copes with the condition.
That is, the generated excessive current is suppressed, and the flickers generated in other illumination devices connected to the power line in common with the heaters can be suppressed.
(2) A heater control apparatus, characterized in that,
the heater control apparatus is provided with: a plurality of switch elements to switch the supply of the electric power from a common power source; a plurality of heaters which are connected to the common power source through the plurality of switch elements, and respectively housed in rollers; a switching control means for controlling so that, by controlling a condition of each switch element, the plurality of heaters can be switched between the serial connection condition and parallel connection condition; and a large current limit element arranged in any position in the path forming the short circuit to the AC power source, corresponding to conditions of the plurality of switch elements.
(14) An image forming apparatus, characterized in that,
the image forming apparatus is provided with: a plurality of switch elements to switch the supply of the electric power from a common power source; a plurality of heaters which are connected to the common power source through the plurality of switch elements, and respectively housed in rollers; a switching control means for controlling so that, by controlling a condition of each switch element, the plurality of heaters can be switched between the serial connection condition and parallel connection condition; and a large current limit element arranged in any position in the path forming the short circuit to the AC power source, corresponding to conditions of the plurality of switch elements.
In this connection, it is preferable that the large current limit element in the above case, is a resistor.
In these inventions, because the large current limit element is arranged in any position in the path forming the short circuit to the AC power source, corresponding to conditions of the plurality of switch elements, in the case where a plurality of heaters which can be switched between the serial connection condition and the parallel connection condition, are provided, when connection conditions of the plurality of heaters are switched, even when the short circuit is formed, the destruction of the switch element due to the dead short is prevented. Accordingly, the heater control apparatus and the image forming apparatus, in which the reliability of operations is high, can be realized.
Further, when the resistor is used for the large current limit element, the complicated switch control or high cost element is not used, and the apparatus in which the desired object is attained by a simple structure and in the low cost, can be structured.
(15) A heater control apparatus, characterized in that,
in the heater control apparatus, which is provided with: a plurality of switch elements to switch the supply of the electric power from a common power source; a plurality of h eaters which are connected to the common power source through the plurality of switch elements, and respectively housed in rollers; a switching control means for controlling so that, by controlling a condition of each switch element, the plurality of heaters can be switched between the serial connection condition and parallel connection condition; and a large current limit element arranged in any position in the path forming the short circuit to the AC power source, corresponding to conditions of the plurality of switch elements,
in the case where one heater is tried to be lighted, the switching control means controls such that, when the temperature of a roller heated by the other heater is in a predetermined temperature range, one heater is serially connected to the other heater, and lighted, and when the temperature of a roller heated by the other heater is not higher than a predetermined temperature range, the one heater is parallelly connected with the other heater, and lighted, and when the temperature of the roller heated by the other heater exceeds the predetermined temperature range, the one heater is independently lighted.
(16) An image forming apparatus, characterized in that,
in the image forming apparatus, which is provided with: a plurality of switch elements to switch the supply of the electric power from a common power source; a plurality of heaters which are connected to the common power source through the plurality of switch elements, and respectively housed in rollers; a switching control means for controlling so that, by controlling a condition of each switch element, the plurality of heaters can be switched between the serial connection condition and parallel connection condition; and a large current limit element arranged in any position in the path forming the short circuit to the AC power source, corresponding to conditions of the plurality of switch elements,
in the case where one heater is tried to be lighted, the switching control means controls such that, when the temperature of a roller heated by the other heater is in a predetermined temperature range, one heater is serially connected to the other heater, and lighted, and when the temperature of a roller heated by the other heater is not higher than a predetermined temperature range, the one heater is parallelly connected with the other heater, and lighted, and when the temperature of the roller heated by the other heater exceeds the predetermined temperature range, the one heater is independently lighted.
In this connection, it is preferable that the large current limit element is a resistor.
In these inventions, in the case where one heater is tried to be lighted,
(a) when the temperature of a roller heated by the other heater is in a predetermined specified temperature range, one heater is controlled in such a manner that it is serially connected to the other heater and lighted,
(b) when the temperature of a roller heated by the other heater is not higher than a predetermined specified temperature range, the one heater is controlled such that it is parallelly connected with the other heater, and lighted, and,
(c) when the temperature of the roller heated by the other heater exceeds the predetermined specified temperature range, it is controlled in such a manner that the one heater is not connected to the other heater and only the one heater is lighted.
When conducted as described above, when a plurality of heaters are lighted in the case of (a), the resistance value is increased by the serial connection, and even when the temperature is low and the resistance value turns on the heater, the rush current is reduced. That is, the generated excessive current is suppressed and the flickers generated in other illumination devices connected to the power line in common with the heaters can be suppressed. Further, in the case of (b), in order to dissolve the low temperature condition, the temperature rise is accelerated by the parallel connection. Further, in the case of (c), the lighting of the other heater is not necessary and only the one heater copes with the condition.
Then, in these inventions, because the large current limit element is arranged in any position in the path forming the short circuit to the AC power source, corresponding to conditions of the plurality of switch elements, in the case where a plurality of heaters which can be switched between the serial connection condition and the parallel connection condition, are provided, when connection conditions of the plurality of heaters are switched, even when the short circuit is formed, the destruction of the switch element due to the dead short is prevented. Accordingly, the heater control apparatus and the image forming apparatus, in which the reliability of operations is high, can be realized.
Further, when the resistor is used for the large current limit element, the complicated switch control or high cost element is not used, and the apparatus in which the desired object is attained by a simple structure and in the low cost, can be structured.